This invention relates to a process for applying a relatively nonviscous liquid to web material, such as textile, in which process the web material is passed through the nip of a pair of rollers, one of which, hereinafter called the intermediate roller, is provided with a film of liquid by means of an applicator roller which is partly immersed in a liquid bath and which rotates in contact with said intermediate roller.
In such a process, for example the applicator roller has a chromium-plated surface, while the intermediate roller in contact with the applicator roller is coated with rubber. This rubber intermediate roller as it were rubs off the applicator roller, so that a thin film of liquid is left behind on the surface of the rubber intermediate roller. This film of liquid is transferred to the web material, which is pressed onto the rubber intermediate roller by the upper roller.
The object of such a manner of applying liquid is to apply an exactly metered small quantity of liquid in even distribution over the surface of the web material. The application of an exactly metered quantity of liquid in even distribution is of great importance for various textile processes. The quantity of liquid applied ranges, for example, from 7.5 to 15 grams per m.sup.2 of material.
In practice it has been found that it is difficult to apply a small, metered quantity of liquid over the surface of the web material in even distribution. The quantity applied is strongly dependent on the peripheral velocity of the rollers, that is, the velocity of passage of the web material.
The invention contemplates a process wherein this drawback is avoided and wherein it is possible to apply the liquid in a small, reproducible dosage.
For this purpose there is used according to the invention an applicator roller, the surface of which is provided with raised portions and recesses. In this way high pressures are avoided in the nip between the applicator roller and the intermediate roller co-acting therewith, so that the two rollers can remain practically in contact with each other over their entire widths independent of the rotation velocity, a suitable nip pressure, falling in the range 0.1 to 0.2 kg/cm. No additional pressure, as for example from hydraulic or pneumatic hold-down cylinders operating on the pins of the top roller is needed. The quantity of liquid transferred as a liquid film to the intermediate roller has a certain thickness which is independent of the velocity of the web and only depends on the surface profile of the applicator roller. The liquids to be applied are generally non-viscous and the use of a doctor blade to remove excess liquid from the intermediate or applicator roller is not needed.
In a preferred embodiment of the process according to the invention there is used an applicator roller having a metal surface provided with cup-shaped recesses. In practice it has been found that the thickness of the liquid film depends on the number and the depth of said cup-shaped recesses, so that in order to obtain a determined, small quantity of liquid in the web material it is only the choice of the right applicator roller that is decisive.
Furthermore, according to the invention, the top roller of the pair of rollers may rest with its own weight on the intermediate roller, which intermediate roller rests on the applicator roller. Surprisingly, it has been found that the pressure resulting from the weights of the rollers promotes uniformity of the liquid distribution. The weight of the top roller and the construction of the top and intermediate roller surfaces should be chosen so that the nip pressure between the two rollers is very light, ordinarily less than approximately 0.2 kg/cm.
The process of the present invention makes it possible to apply any desired quantity of liquid to the web material by employing a plurality of applicator rollers, each of which transfers a determined standard quantity of liquid. This is advantageous in that small quantities of liquid, applied at intervals, still further increase the already high uniformity, because the absorption capacity of textile may set restrictions to the quantity of liquid that can be uniformly applied by means of one nip. According to the invention the web material can accordingly be passed through a plurality of pairs of rollers, each comprising one roller arranged to co-act with an applicator roller designed to transfer a determined quantity of liquid.
In order to avoid the occurrence of an asymmetric moisture gradient in the direction of the thickness of the web material, according to another feature of the invention the liquid can successively be applied to both sides of the web material by running the web through a plurality of pairs of rollers.
Furthermore, the invention relates to an apparatus for applying liquid to web material, such as textile, which comprises a pair of rollers forming a nip through which the web material can be passed, and an applicator roller which can rotate partly immersed in a liquid bath and which can co-act with one of said pair of rollers for transferring liquid thereto. According to the invention the apparatus is characterized in that the applicator roller has a surface which is provided with raised portions and/or recesses.
According to the invention there may be provided cup-shaped recesses in the surface of the applicator roller, which ensures a proper control of the quantity of liquid to be applied.
Furthermore, according to the invention the rollers and the applicator roller may be freely rotatable. The advancing web material will then drive all the rollers as it travels through them, so that no further drive means are required. Consequently, the apparatus can easily be fitted at a desired location in a web treating process.
Moreover, according to the invention, the apparatus may comprise a plurality of pairs of rollers, through which the web material can be passed, each pair of rollers being adapted to transfer a determined quantity of liquid to the web and at least one pair of rollers being disengageable by spacing the nip, so that the other pairs of rollers together apply the desired quantity of liquid.